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GHSA-3WX3-9XWG-38FF

Vulnerability from github – Published: 2026-10-18 18:31 – Updated: 2026-10-18 18:31

Details

In the Linux kernel, the following vulnerability has been resolved:

ipv6: Prevent rt6_insert_exception() for dying fib6_info.

Before the cited commit, fib6_nh_flush_exceptions() always set from->exception_bucket_flushed = 1 under rt6_exception_lock to prevent rt6_insert_exception() from inserting a new exception for a dying fib6_info.

The flag was replaced with the FIB6_EXCEPTION_BUCKET_FLUSHED bit stored in nh->rt6i_exception_bucket.

The problem is that now the bit is only set when the bucket is not NULL and fib6_nh_flush_exceptions() is called from fib6_nh_release() after fib6_ref has already reached zero.

If rt6_insert_exception() is called while the target fib6_info is being removed via fib6_purge_rt(), a new exception could be created successfully because rt6_flush_exceptions() no longer sets the bit.

This creates a reference cycle between the fib6_info and the exception route, leaking the fib6_info, its nexthop device, and all per-CPU routes in fib6_nh->rt6i_pcpu, which stalls netdev unregistration.

[ 34.680602] unregister_netdevice: waiting for gre6 to become free. Usage count = 68 [ 44.920675] unregister_netdevice: waiting for gre6 to become free. Usage count = 68 [ 55.176582] unregister_netdevice: waiting for gre6 to become free. Usage count = 68

Let's call fib6_drop_pcpu_from() before rt6_flush_exceptions(), to set fib6_destroying before rt6_exception_lock, and check f6i->fib6_destroying in rt6_insert_exception().

Note that FIB6_EXCEPTION_BUCKET_FLUSHED logic is dead and we can clean it up in net-next.

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{
  "affected": [],
  "aliases": [
    "CVE-2026-98598"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-10-18T16:17:12Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nipv6: Prevent rt6_insert_exception() for dying fib6_info.\n\nBefore the cited commit, fib6_nh_flush_exceptions() always set\nfrom-\u003eexception_bucket_flushed = 1 under rt6_exception_lock to\nprevent rt6_insert_exception() from inserting a new exception\nfor a dying fib6_info.\n\nThe flag was replaced with the FIB6_EXCEPTION_BUCKET_FLUSHED\nbit stored in nh-\u003ert6i_exception_bucket.\n\nThe problem is that now the bit is only set when the bucket\nis not NULL and fib6_nh_flush_exceptions() is called from\nfib6_nh_release() after fib6_ref has already reached zero.\n\nIf rt6_insert_exception() is called while the target fib6_info\nis being removed via fib6_purge_rt(), a new exception could be\ncreated successfully because rt6_flush_exceptions() no longer\nsets the bit.\n\nThis creates a reference cycle between the fib6_info and the\nexception route, leaking the fib6_info, its nexthop device,\nand all per-CPU routes in fib6_nh-\u003ert6i_pcpu, which stalls netdev\nunregistration.\n\n[   34.680602] unregister_netdevice: waiting for gre6 to become free. Usage count = 68\n[   44.920675] unregister_netdevice: waiting for gre6 to become free. Usage count = 68\n[   55.176582] unregister_netdevice: waiting for gre6 to become free. Usage count = 68\n\nLet\u0027s call fib6_drop_pcpu_from() before rt6_flush_exceptions(),\nto set fib6_destroying before rt6_exception_lock, and check\nf6i-\u003efib6_destroying in rt6_insert_exception().\n\nNote that FIB6_EXCEPTION_BUCKET_FLUSHED logic is dead and\nwe can clean it up in net-next.",
  "id": "GHSA-3wx3-9xwg-38ff",
  "modified": "2026-10-18T18:31:55Z",
  "published": "2026-10-18T18:31:55Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98598"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/0346ec2f080b40d95ed05b853bb9226289e75212"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/649ffc76ed5483b2caf35ed90d3787538efc4e53"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/e03e77071e75ce726d877f0a4349a28b6e1f487a"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}

CVE-2026-98598 (GCVE-0-2026-98598)

Vulnerability from cvelistv5 – Published: 2026-10-18 15:19 – Updated: 2026-10-19 09:22

Title

ipv6: Prevent rt6_insert_exception() for dying fib6_info.

Summary

In the Linux kernel, the following vulnerability has been resolved: ipv6: Prevent rt6_insert_exception() for dying fib6_info. Before the cited commit, fib6_nh_flush_exceptions() always set from->exception_bucket_flushed = 1 under rt6_exception_lock to prevent rt6_insert_exception() from inserting a new exception for a dying fib6_info. The flag was replaced with the FIB6_EXCEPTION_BUCKET_FLUSHED bit stored in nh->rt6i_exception_bucket. The problem is that now the bit is only set when the bucket is not NULL and fib6_nh_flush_exceptions() is called from fib6_nh_release() after fib6_ref has already reached zero. If rt6_insert_exception() is called while the target fib6_info is being removed via fib6_purge_rt(), a new exception could be created successfully because rt6_flush_exceptions() no longer sets the bit. This creates a reference cycle between the fib6_info and the exception route, leaking the fib6_info, its nexthop device, and all per-CPU routes in fib6_nh->rt6i_pcpu, which stalls netdev unregistration. [ 34.680602] unregister_netdevice: waiting for gre6 to become free. Usage count = 68 [ 44.920675] unregister_netdevice: waiting for gre6 to become free. Usage count = 68 [ 55.176582] unregister_netdevice: waiting for gre6 to become free. Usage count = 68 Let's call fib6_drop_pcpu_from() before rt6_flush_exceptions(), to set fib6_destroying before rt6_exception_lock, and check f6i->fib6_destroying in rt6_insert_exception(). Note that FIB6_EXCEPTION_BUCKET_FLUSHED logic is dead and we can clean it up in net-next.

Severity

No CVSS data available.

Assigner

Linux CNA under the mitre root

CNA scorecard D 53/100 over 6820 records in the last 180 days details

References

3 references

URL	Tags
https://git.kernel.org/stable/c/649ffc76ed5483b2c…
https://git.kernel.org/stable/c/e03e77071e75ce726…
https://git.kernel.org/stable/c/0346ec2f080b40d95…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: cc5c073a693fa6ed7a207b0436114f68cce72434 , < 649ffc76ed5483b2caf35ed90d3787538efc4e53 (git) Affected: cc5c073a693fa6ed7a207b0436114f68cce72434 , < e03e77071e75ce726d877f0a4349a28b6e1f487a (git) Affected: cc5c073a693fa6ed7a207b0436114f68cce72434 , < 0346ec2f080b40d95ed05b853bb9226289e75212 (git)
Linux	Linux	Affected: 5.3 Unaffected: 0 , < 5.3 (semver) Unaffected: 6.18.55 , ≤ 6.18.* (semver) Unaffected: 7.2.9 , ≤ 7.2.* (semver) Unaffected: 7.3 , ≤ * (original_commit_for_fix)

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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/ipv6/ip6_fib.c",
            "net/ipv6/route.c"
          ],
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          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "649ffc76ed5483b2caf35ed90d3787538efc4e53",
              "status": "affected",
              "version": "cc5c073a693fa6ed7a207b0436114f68cce72434",
              "versionType": "git"
            },
            {
              "lessThan": "e03e77071e75ce726d877f0a4349a28b6e1f487a",
              "status": "affected",
              "version": "cc5c073a693fa6ed7a207b0436114f68cce72434",
              "versionType": "git"
            },
            {
              "lessThan": "0346ec2f080b40d95ed05b853bb9226289e75212",
              "status": "affected",
              "version": "cc5c073a693fa6ed7a207b0436114f68cce72434",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
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          ],
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          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "5.3"
            },
            {
              "lessThan": "5.3",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.55",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.9",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.55",
                  "versionStartIncluding": "5.3",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.9",
                  "versionStartIncluding": "5.3",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3",
                  "versionStartIncluding": "5.3",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nipv6: Prevent rt6_insert_exception() for dying fib6_info.\n\nBefore the cited commit, fib6_nh_flush_exceptions() always set\nfrom-\u003eexception_bucket_flushed = 1 under rt6_exception_lock to\nprevent rt6_insert_exception() from inserting a new exception\nfor a dying fib6_info.\n\nThe flag was replaced with the FIB6_EXCEPTION_BUCKET_FLUSHED\nbit stored in nh-\u003ert6i_exception_bucket.\n\nThe problem is that now the bit is only set when the bucket\nis not NULL and fib6_nh_flush_exceptions() is called from\nfib6_nh_release() after fib6_ref has already reached zero.\n\nIf rt6_insert_exception() is called while the target fib6_info\nis being removed via fib6_purge_rt(), a new exception could be\ncreated successfully because rt6_flush_exceptions() no longer\nsets the bit.\n\nThis creates a reference cycle between the fib6_info and the\nexception route, leaking the fib6_info, its nexthop device,\nand all per-CPU routes in fib6_nh-\u003ert6i_pcpu, which stalls netdev\nunregistration.\n\n[   34.680602] unregister_netdevice: waiting for gre6 to become free. Usage count = 68\n[   44.920675] unregister_netdevice: waiting for gre6 to become free. Usage count = 68\n[   55.176582] unregister_netdevice: waiting for gre6 to become free. Usage count = 68\n\nLet\u0027s call fib6_drop_pcpu_from() before rt6_flush_exceptions(),\nto set fib6_destroying before rt6_exception_lock, and check\nf6i-\u003efib6_destroying in rt6_insert_exception().\n\nNote that FIB6_EXCEPTION_BUCKET_FLUSHED logic is dead and\nwe can clean it up in net-next."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T09:22:24.055Z",
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        "shortName": "Linux"
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        },
        {
          "url": "https://git.kernel.org/stable/c/0346ec2f080b40d95ed05b853bb9226289e75212"
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  "cveMetadata": {
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    "cveId": "CVE-2026-98598",
    "datePublished": "2026-10-18T15:19:11.126Z",
    "dateReserved": "2026-09-25T10:25:14.359Z",
    "dateUpdated": "2026-10-19T09:22:24.055Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
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Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

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